Cooling systems such as refrigerators, freezers, air conditioners and others, are used to cool environments and/or to freeze different kinds of products for consumption. These devices usually remain connected for long periods of time and consume large quantities of energy. Therefore, nowadays it is an ongoing concern for manufacturers of this kind of equipment to develop mechanisms that reduce energy consumption as much as possible whilst at the same time maintaining cooling efficiency.
All cooling equipments comprise a cooling circuit whose function is to maintain the low temperature inside the cooled space. This cooling circuit is a closed circuit, through which a cooling fluid circulates, and is essentially comprised of a hermetic compressor, a condenser, a pressure control device and an evaporator. When the cooling fluid in liquid state passes through the evaporator, it absorbs heat from the environment to be cooled, and transforms itself into vapor. Next, the fluid in vapor state originating from the evaporator is sent to the compressor, whose function is to compress the fluid and cause it to circulate in the circuit. Afterwards, the heated fluid in vapor form passes through the condenser, where it is converted into liquid state, releasing heat to the external environment. Next, the fluid circulates towards the pressure control device, where it undergoes a drop in pressure. The function of this device is to control the pressure of the cooling fluid to be sent to the evaporator. This cooling cycle repeats continually for as long as the cooling equipment is running.
Besides the basic components described above, cooling systems usually also have ventilators mounted near the evaporator and the condenser, cooling flow control valves, air flow control dampers and lamps mounted inside and outside the cooled space.
Cooling systems also include a control system for controlling the operations of some of the cooling system components. The purpose of this control system is to guarantee that the temperature inside the cooled space is kept at the desired values, even when variations occur in the external conditions of the cooler, for example, an increase in room temperature or, in the case of refrigerators or freezers, frequent door openings of the appliance causing the temperature of the cooled space to rise.
Manufacturers of cooling systems have constantly sought to develop improvements in control systems so that they maintain the temperature conditions inside the cooled space and, at the same time, provide improved conditions of use for the different cooling system components. Said conditions include operations with lower energy consumption, and working conditions that do not cause wear and tear of the component parts, providing increased durability of the equipment.
The control systems currently applied to cooling systems use a central processing unit that receives signals from the cooling system sensors, such as thermopars, thermistors, current sensors, door-opening sensors, movement sensors, etc. The function of these sensors is to detect the working conditions of the cooling system components and/or general characteristics of the cooled space and the external environment. Therefore, each sensor is installed in the different environments where it is desirable to control the conditions, or else is attached directly to the cooling system components themselves. For instance, pressure and temperature sensors are installed in the evaporator, condenser and flow control device in order to measure the pressure and temperature inside these equipments.
Based on the values measured by these and other sensors, the operation of the cooling system is controlled. The signals originating from the sensors, corresponding to physical and electrical variables, are processed by the central processing unit, which interprets the parameter variation detected by each sensor in isolation. Next, the central processing unit generates control signals for each component of the cooling system, solely based on the relative parameter values from each cooling system component in isolation.
Based on this control architecture of the cooling system, the control of the working conditions of each cooling system component is performed solely based on the measurement of the physical and electrical variables that are directly related to the operation of this same component. No broader evaluation is made on the general operation of the cooling system, in order to identify the interdependency existing in the operation of the system components. In other words, the control is carried out on a local and individual basis, not on a more all-embracing or integrated basis, searching to optimize the operation of all components simultaneously.
Additionally, this kind of control system requires the use of at least one sensor to detect the working conditions of each cooling system component. Consequently, this kind of circuit has the disadvantage of being rather complex, in view of the number of connections and wiring required for installment, and it is also costly due to the need for a large quantity of sensors and because of the various assembly steps applied in the production lines of cooler appliances.
An example of a temperature control system of a cooling or heating appliance from the state of the art based on the use of sensors, designed to reduce the consumption of energy of the appliance, is described in document U.S. Pat. No. 6,745,581. According to this North-American patent, the system is designed for drink dispensers wherein the temperature at the point of consumption needs to be quite low, in the case of cooled drinks, or quite high in the case of hot drinks. This control system comprises sensors designed to detect the conditions on the outside of the appliance, such as movement sensors for persons in the proximity of the cooling appliance and door-opening sensors that are connected to a central processing unit which controls the operation of the appliance. The conditions detected and recorded by the control system are related to activities around the appliance that are indicative of the use thereof. Consequently, the control system learns functional patterns (standards) associated to the schedules of use of the appliance, and establishes a low energy consumption program over a specific time period based on the functional patterns learned. The control system is able to control the cooling system to start lowering the temperature of the cooled space with the required antecedence for products inside it to reach the temperature most suitable for consumption at the point in which consumption movement begins.
This temperature control system is solely intended for cooling appliances that have no need to maintain a constantly low temperature in the cooled space, required to conserve food products. Therefore, during times when there is no consumption of the products stored in the appliance, the temperature in the cooled space can be kept higher in order to reduce energy consumption.
Additionally, the control system according to this patent application requires the use of sensors designed to read physical variables outside the cooler, such as door-opening sensors, movement sensors, vibration detectors and others. Detecting movement and learning the patterns of use of the appliance cannot be based on measurements of electrical variables related to the cooling system components themselves.
Nor does this control system carry out an integrated control over the operation of the cooling system components. Controlling the cooling system is solely based on activity conditions from outside the cooling appliance.